This invention relates to methods for improved separation and de-watering of process muds, such as muds from paper mills, and for removing contaminants, color, and total organic carbon (TOC) from process waste waters prior to their discharge into waterways.
Process muds include processing water and various solids that are generated in processing plants, such as paper mill plants. This processing water must be separated from process muds prior to discharging the water to public or private waterways. The remaining solids are separately disposed of. These solids include finely divided solid particles that can be difficult to filter. De-watering of these muds is generally required due to their high water content and because many landfills have maximum requirements for water content. De-watering comprises separation of the water from the solid particles. Solids desirably are agglomerated to form a floc, or fairly large aggregates, that can be readily filtered and separated from the waste water.
Various industrial processes produce highly colored waste waters, which can vary from yellow to dark brown. Color bodies vary widely as to their source and their depth of color. Waters that are produced by the digestion of cellulosic fibers, pulp fibers, for example, from water processing during paper making, are washed several times, producing aqueous streams containing digestion chemicals, lignins, sugars, bleach or chlorine-containing chemicals, dyes, fillers, starches, and the like. A paper mill that produces 500 tons of paper per day can produce more than 20 million gallons per day of waste effluent streams. Colored solid particles in suspension in such waste water can be removed by filtration or settling. However, if the color bodies are in true solution, they are more difficult to remove. Obviously, highly colored waste waters must be treated prior to discharging them into municipal waters or natural streams, to remove any toxic compounds, and those compounds that add a smell or taste to the water.
In addition, other materials present in these muds include phosphorus, which is also a regulated contaminant, and metal salt coagulants, including heavy metal salts that are required to be removed from waste waters prior to their discharge into public waterways.
Increasingly stringent environmental regulations must be complied with as well. The color bodies present in these muds are of various types, depending on the source of the water, the process that produces these muds, and any treatments used to remove the color bodies.
Fuller, U.S. Pat. No. 3,627,679 , developed a process to remove color bodies wherein the waste water is mixed with alum process residues (APR) and allowed to settle. However, the settling time is quite lengthy for the amount of color removed, and there are mechanical difficulties associated with filtering the resultant mixture.
U.S. Pat. No. 5,766,485 to Lind et al discloses a color removal treatment for paper and pulp wastewater streams comprising adding polyelectrolytes to alum process residues obtained from producing aluminum sulfate from bauxite clays. The addition of these polyelectrolytes and water-soluble polymers increases the sedimentation rate of solid particles in waste waters, and alum process residues are added to remove the color bodies. The reduction of organic residues is also highly desirable. However, these materials often must be added in large doses, which adds to the costs of process muds treatment.
Thus a method that both improves the de-watering of process muds and sludges, and also removes color and organic materials from the separated water, would be highly desirable.
We have found that high clay alumina, (HCA), a co-product of the manufacture of aluminum sulfate from bauxite, is an excellent de-watering material. The HCA is mixed with plant sludges or muds, optionally together with a selected polymer and/or alum process residue (APR), in an amount so as to cause de-stabilization and flocculation of the solid particles. The floc and waste waters are separated, as by filtration. Surprisingly, not only excellent de-watering and sludge release are obtained by the addition of HCA, but color, organic materials and heavy metals are removed from the waste water filtrate as well. Other salts, such as iron or aluminum salts, can be added to the muds or sludges for purposes of odor control or phosphorus precipitation. Further, these additives reduce the generation of disinfection by-products in potable water supplies and also those compounds that cause color and odor.